Trials of two new drugs for bancroftian filariasis have been initiated with collaborators in Madras, India. Ivermectin (Phase IIa) at doses between 25-200 mcg/kg once orally has been found to be a rapid, extremely effective microfilaricide, but my three months the microfilarial load has returned to about 10% of pretreatment levels. Therefore its adult-filaricidal potential requires additional evaluation as does the importance of side reactions associated with the rapid death (first 12-24 hours) of the microfilariae. CGp 20376 (Phase I) has been successfully given to normals in doses from 0.01-1.0 mg/kg once orally without any significant side effects. Its filaricidal activity in man must now be evaluated. Because long-term follow-up studies employing bronchoalveolar lavage to evaluate patients treated conventionally with diethylcarbamazine (DEC) have shown that less than 1/3 relapse or have persistent low-grade alveolitis leading to pulmonary fibrosis, a therapeutic trial of three regimens (conventional DEC, long-term DEC, or DEC + steroids) has been initiated in Madras. The study will require about three years to enroll the anticipated 75 study patients. Observations on 200 Peace Corps volunteers going to Loa loa endemic areas of Africa are concluding after two years of a placebo-controlled chemoprophylaxis trial using weekly doses of DEC. Seroconversion is at about 15%, but the placebo vs. drug code will not be broken until October, 1986, so that the success of the prophylactic regimen cannot yet be determined.